In the art of oil well pumping it is well known to provide a motor driven pumping jack for lifting oil in discreet slugs or pulses from the pocket at the bottom of the well bore to the surface. Such a pumping system typically comprises a power driven jack or beam which reciprocates on a pivot to reciprocate a string of well rod up and down in the well casing. A working barrel is connected to the well rod string adjacent its lowermost end for reciprocation in unison therewith within the well pocket to thereby provide the lifting or pumping action which delivers the crude oil and brine from the well pocket to the head at the surface, and thence via suitable production piping to a holding tank or similar storage facility.
The rate at which the crude oil in an oil well migrates to the well bore and fills the well pocket may vary widely from one well to another depending upon specific geologic conditions in the oil bearing sands, and the age of the oil field in terms of the proportion of recoverable crude oil which has been removed from the geologic formations. In mature wells, commonly known as stripper wells, the maximum attainable production rate will depend entirely on how quickly the spontaneous migration of crude oil to the well pocket can fill the pocket. Typically, in such wells the pumping capacity of the pumping jack is far greater than the capacity of the field to refill well pocket with crude oil from the oil bearing formations. Even in newer, more productive wells the pumping capacity of the pumping jack may far exceed spontaneous well pocket refill rates.
To accommodate these and other conditions and limitations of oil well production, practitioners of the art have proposed numerous systems for controlling well production. For example, U.S. Pat. No. 1,754,946 discloses a pressure differential control valve system for use in the control of well flow. U.S. Pat. No. 3,276,380 discloses a mechanical float in a float chamber which is operable according to the level of fluid within the float chamber to influence pump operation responsive to a reduction of the volume of fluid passing through the production conduit at the earth's surface. U.S. Pat. No. 3,050,003 discloses a pressure actuated valve which operates switch contacts to control a well pump motor. U.S. Pat. No. 3,274,940 discloses a well pump control system with a float chamber connected to the production piping upstream of a pressure control valve to control pump motor operation. Also disclosed is a conduit apparently for equalizing pressure on upstream and downstream sides of the pressure control valve.
Other patents which typify the prior art include U.S. Pat. Nos. 4,329,120 (protector apparatus for a down hole pump), 3,614,761 (flow sensors for a drilling mud circulation system), 3,559,731 (adjustable timed off cycles in a well pump control system), 3,072,059 (a flow control valve with electrical contacts that are utilized to control a pump motor), 3,568,771 (controlling pump RPM as a function of the crude oil bulk density) and 2,944,488 (pump control system including a venturi for maintaining constant fluid pressure in a flow conduit.
There remains in the art a need for improved control of pumping jack operation to control pumping time in a manner that the pumping jack does not continue to operate when a well is pumped off, that is when the well pocket is dry. It is desirable that pump operation be terminated at the end of the normal productive pumping cycle of an oil well when the flow rate of fluid to the surface has decreased and level of fluid in the pocket is low. Without effective control of pumping jack operation, the jack will continue to pump when there is not sufficient fluid above the working barrel in the well pocket. This would result in increased crude oil production costs and wear and tear on the pumping mechanism.
Additionally, in many producing fields today, multiple wells are connected to a single stock tank such that the head pressure against which the pumping jack must work in any given well may be constantly changing. This can present production control problems, especially in systems that are balanced for production at a uniform pressure condition. The prior art has not provided entirely satisfactory solutions to the above-characterized and other production problems.